KAUFMAN, Texas (CNN) — Kaufman County is on edge. Two prosecutors killed in two months, including the district attorney, gunned down in his home over the weekend.

What’s going on? Is someone assassinating prosecutors?

As armed guards surround the Kaufman County Courthouse and police shrouded some public officials in around-the-clock protection, it seems there are as many questions as answers.

Several dozen FBI agents are now assisting the investigation, a bureau spokeswoman said.

District Attorney Mike McLelland and his wife, Cynthia, were shot to death, nearly two months after one of his assistants died in a brazen daytime shooting outside the north Texas county’s courthouse. Rifle casings littered the scene, according to a law enforcement source.

A search warrant affidavit stated the couple was found dead Saturday evening by friends who had tried to reach them several times during the day. Each of them had been shot multiple times, the affidavit states.

McLelland talked to relatives on Friday night, the affidavit states. Investigators have asked a judge for records of mobile phone calls that were relayed through at least one nearby tower, the documents show.

The killings followed warnings that a white supremacist group might be preparing to take revenge on law enforcement officials who targeted them in 2012. Both Kaufman County prosecutors apparently started carrying guns, but it wasn’t enough.

It’s unclear whether the killings were linked to the January 31 shooting death of Kaufman County assistant prosecutor Mark Hasse, or to the March 19 death of the prisons chief in Colorado. Authorities say a suspect in that shooting was a onetime white supremacist gang member who died in a shootout with deputies — in north Texas.

“This whole thing is shocking to all of us,” said Kaufman County Judge Bruce Wood during a Monday news conference. “I would be less than honest if I told you I was not worried.”

Attorney Pete Schulte, who has worked in the county, said, “The law enforcement community here is very uncomfortable. It’s really sending some shock waves through the community.”

McLelland’s office was closed Monday, but other Kaufman County courthouse offices reopened under heavy security. Brandi Fernandez, McLelland’s first assistant district attorney, will take over the office on an interim basis until Gov. Rick Perry can appoint a successor, county officials announced.

In a statement issued earlier in the day, Perry offered his condolences to McLelland’s family and friends and promised to name a replacement “as soon as possible.”

Latest shooting

The McLellands’ bodies were found Saturday at their home in the Dallas suburb of Forney. Authorities haven’t said much about what happened beyond that.

A law enforcement source told CNN that investigators have recovered several shell casings from a .223-caliber rifle.

Mike Griffith, whose yard backs up to the McLellands’, told CNN affiliate WFAA-TV he thinks he heard the attack unfolding early Saturday.

“It was five or six shots, one right after the other,” WFAA quoted Griffith as saying.

The deaths came almost exactly two months after someone shot Hasse and the day McLelland vowed to bring his killer — he used the word “scum” — to justice.

“We’re going to pull you out of whatever hole you’re in, we’re going to bring you back and let the people of Kaufman County prosecute you to the fullest extent of the law,” he said.

Hasse had feared for his life and carried a gun to work, said a Dallas attorney who described herself as his longtime friend.

Colleen Dunbar said she spoke with Hasse a week before he died. She said the prosecutor told her he had begun carrying a gun in and out of the county courthouse daily.

“He told me he would use a different exit every day because he was fearful for his life,” Dunbar told CNN.

She said that Hasse gave no specifics on why he felt threatened, only that he did.

Are killings retribution?

Authorities insist that they just don’t know who may be behind the killings. “I have no idea who’s responsible,” Wood said.

However, McLelland’s office was one of numerous Texas and federal agencies involved in a multiple-year investigation that led to the 2012 indictment of 34 alleged members of the Aryan Brotherhood of Texas, including four of its senior leaders, on racketeering charges.

At the time, Assistant U.S. Attorney Lanny A. Breuer called the indictment a “devastating blow” to the organization, which he said used threats and violence, including murder, against “those who violate (its) rules or pose a threat to the enterprise.”

The FBI describes the group as a “whites only,” prison-based gang with members operating inside and outside of state and federal prisons throughout Texas and elsewhere in the United States since at least the early 1980s.” Its members have been involved in at least three murders, according to federal authorities.

While authorities have not said whether they have established a link between the deaths of Hasse and McLelland, or the involvement of white supremacists, Texas law enforcement agencies did warn shortly after the November 2012 indictment that there was “credible information” that members of the Aryan Brotherhood were planning to retaliate” for the indictment.

U.S. Rep. Ted Poe told CNN that the killings could have been the work of the group.

“The district attorney has said they operate in his portion of the state of Texas,” Poe told CNN. “It seems that a scenario may be developing that the district attorney’s office was investigating this gang or another gang and they wanted to prevent that investigation and therefore they resort to violence.”

Kaufman County Judge Bruce Wood said Monday that no physical evidence links McLelland’s death and Hasse’s, although previously he had said he believes there is a “strong connection” between the killings.

Kaufman Mayor William Fortner went further, saying he believes the men were targeted for revenge.

“That’s the logical conclusion, and I don’t have any information that directs me to think that’s the case, but that’s what you would assume under the circumstances, since they targeted two people from our prosecutors,” he said.

In an interview with The Associated Press after Hasse’s death, McLelland said his deputy hadn’t been involved in the Aryan Brotherhood of Texas investigation. But the district attorney nevertheless raised the possibility the group was behind his death.

“We put some real dents in the Aryan Brotherhood around here in the past year,” McLelland told the news agency.

In the AP interview, McLelland said he, too, began carrying a gun after Hasse’s death and was answering his door more carefully.

Colorado slaying

As if the potential links between Hasse and McLelland’s shootings weren’t enough, speculation has also extended to whether the shootings have any connection to the March 19 death of Colorado prisons chief Tom Clements, who was gunned down after answering the door to his house.

While authorities have offered no suggestion the crimes are linked, the man suspected of killing Clements was once a member of a white supremacist group, the 211 Crew. That man, Evan Ebel, died in a shootout with sheriff’s deputies in northern Texas.

Other explanations

The white supremacist angle is just one of many possibilities, the Dallas Morning News quoted McLelland’s former boss in the Dallas public defender’s office as saying.

“It could be local meth lab people down there in Kaufman County, it could be Mexican cartel, it could be the Aryan Brotherhood,” the newspaper quoted Former Dallas Chief Public Defender Brad Lollar as saying. “Or it could just be someone with a personal grudge.”

‘On heightened alert’

Regardless of the motive, the killings have left law enforcement officials and residents in the county nervous.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives joined Texas Rangers, the FBI and local authorities in investigating the killing of McLelland and his wife, the agency’s Dallas office spokesman, Andrew Young, told CNN.

Several dozen FBI agents and support staff are now assisting the investigation into the killings, said Katherine Chaumont, a spokeswoman for the bureau’s Dallas field office. Agents are working at the investigation’s command post, helping out with interviews and checking for any useful surveillance video, though Chaumont said she was unaware whether any had been found.

In Houston, Harris County Sheriff Adrian Garcia put District Attorney Mike Anderson and his family under 24-hour security in the wake of McLelland’s death, said Sara Marie Kinney, a spokeswoman for the prosecutor’s office. Anderson’s office was part of the same task force as Kaufman County authorities.

Uniformed officers have also been placed outside Anderson’s office, she said.

Mayor Fortner said Monday on CNN’s “Starting Point” that the fear is pervasive.

“I wonder if the governor is going to find anyone brave enough to take the job of district attorney,” he said.